Hiroshima marked the 69th anniversary of the U.S. atomic bombing Wednesday, as survivors of the attack and others gathered at the city's Peace Memorial Park early in the morning to pay their respects and to attend an annual ceremony commemorating the event.

At the ceremony, held just a few hundred meters from the hypocenter of the bombing, Hiroshima Mayor Kazumi Matsui called on Prime Minister Shinzo Abe's government to work to bridge the gap between nuclear weapons states and the rest of the world in the quest for global nuclear disarmament.

While refraining from directly mentioning his stance on collective self-defense, an issue that sharply divides peace advocates, Matsui said that, "precisely because our security situation is increasingly severe, our government should accept the full weight of the fact that we have avoided war for 69 years thanks to the noble pacifism of the Japanese Constitution."

The anniversary comes ahead of next year's review of the Nuclear Non-Proliferation Treaty, the cornerstone of the international nuclear disarmament regime.

Attendees at the ceremony this year included Abe, U.S. Ambassador to Japan Caroline Kennedy, and representatives from 67 other countries, including nuclear powers Britain, France and Russia, according to city officials.

On Aug. 6, 1945, the U.S. bomber Enola Gay dropped an atomic bomb on Hiroshima, ushering in the nuclear age. The bomb, nicknamed "Little Boy," detonated at 8:15 a.m. at an altitude of about 600 meters, leaving an estimated 140,000 people dead by the end of the year.

A second atomic bomb was dropped on Nagasaki on Aug. 9 of that year. Japan surrendered to Allied Forces six days later, bringing an end to World War II.

The number of hibakusha from both bombings living in Japan and abroad stood at 192,719 as of late March, falling below 200,000 for the first time. Their average age was 79.44.